1. Field of the Invention
The present invention relates to a receiving circuit suitable for use in a radio apparatus using a TDMA (Time Division Multiple Access) or the like.
2. Description of the Related Art
In a digital mobile communication, a frame used as a fundamental cycle or period is determined and a radio signal is transmitted and received by using constant time widths (called principally “time slots”) assigned within the frame.
Therefore, radio lines or circuits using the same frequency can be used on a time-sharing basis. Thus, respective stations, which perform communications, respectively have a common time base and allows a transmitted radio signal to have synchronizing patterns (also called “unique words”) as information to be used in the respective stations as time bases, thereby making it possible to perform timing control so that they do not overlap each other over the radio lines.
Namely, a transmitting side (e.g., a base station) modulates digital data to be transmitted and transmits burst signals each represented in a predetermined format, which include the modulated data and synchronizing patterns, as a radio signal. A receiving side (e.g., a mobile station) demodulates the received radio signal and detects the corresponding synchronizing pattern from data (hereinafter called “demodulated data”) demodulated therein. When the synchronizing pattern is detected, the data is stored based on clock signals for storing and outputting the demodulated data with the synchronizing pattern as the time base. Owing to the detection of the synchronizing pattern, it is possible to determine which position of the demodulated data corresponds to desired data.
The stored data is outputted to an external microcomputer and a superior circuit and subjected to desired processing according to purposes.
On the other hand, when no synchronizing pattern is detected, the previously-received and stored data or data in which all the bits are fixed to logical “0” or “1”, is outputted to the external microcomputer and the superior circuit.
A bit error rate characteristic might be measured by a wireless or radio apparatus. The bit error rate characteristic is one obtained by receiving a ratio between a radio signal and noise as a parameter and measuring to which extent each demodulated data would err. Measuring the bit error rate characteristic makes it possible to determine the quality of digital transmission made between two stations for performing transmission and reception.
Upon the measurement of the bit error rate characteristic, the transmitting side, e.g., a test signal generator transmits modulated data comprised of a pseudo random pattern based on a predetermined law, which is called “pseudo random pattern”, together with a synchronizing pattern as data modulated in each transmitted burst signal.
The receiving side, e.g., the mobile station receives and demodulates the transmitted burst signal. A receiving or receiver circuit on the receiving side detects a synchronizing pattern from demodulated data. When the synchronizing pattern is detected, data equivalent to a pseudo random pattern can be stored in the receiving circuit from the demodulated data. The stored data is outputted to, for example, a testing device or the like. The testing device confirms in bit units whether the stored data is based on a law used to generate the pseudo random pattern upon transmission. Of the received data, bits non-based on the law used to generate the pseudo random pattern upon transmission are counted as errors. A bit error rate characteristic is measured based on the counted number.
Here, the transmitting side divides the continuous pseudo random pattern over continuous plural frames by predetermined burst signals for the respective frames and transmits the divided ones therefrom. Therefore, when the receiving circuit is not able to detect the corresponding synchronizing pattern from demodulated data of each transmitted burst signal, it cannot extract data corresponding to a pseudo random pattern from the demodulated data in the burst signal. Therefore, each burst signal from which no synchronizing pattern could not be detected, could lead to an about 50% probability of error. As a result, a correct bit error rate characteristic cannot be measured.
An object of the present invention is to provide a receiving circuit capable of solving the foregoing problems and more accurately measuring a bit error rate characteristic.
Another object of the present invention is to provide a receiving circuit which reduces the influence exerted on a normal operation thereof, an increase in the number of components constituting the receiving circuit, and an increase in power consumption as small as possible to thereby realize the above object.